It is possible to access Elastic Map Service’s files via the same mechanism

url: {
// "type" defaults to "elasticsearch" otherwise
type: emsfile
// Name of the file, exactly as in the Region map visualization
name: World Countries
}
// The result is a geojson file, get its features to use
// this data source with the "shape" marks
// https://vega.github.io/vega/docs/marks/shape/
format: {property: "features"}